1. Field of the Invention
The present invention relates to a heat transfer apparatus utilizable in heating a room, for example, by circulating a refrigerant, such as halogenated hydrocarbon HCFC 22, heated by a heat source such as an oil or gas burner through a radiator by the utilization of changes in pressure of the refrigerant and its gravitational effect. More particularly, the present invention relates to a compact and inexpensive heat transfer apparatus having a simple construction and an increased reliability and also having an increased heat transfer efficiency.
2. Description of Related Art
A heat transfer apparatus of this kind is well known from Japanese Laid-open Patent Publication (unexamined) No. 3-51631 and will be described below with reference to FIGS. 1A and 1B.
The heat transfer apparatus shown therein comprises a container 1 made up of two members soldered to each other. The container 1 is disposed above a refrigerant heater 4 having a burner 19. An upper portion of the container 1 functions as a gas-liquid separating chamber 2, while a lower portion thereof functions as a reservoir for storing liquid refrigerant 3. The container 1 is fluid-connected with the refrigerant heater 4 via an inlet pipe 5 extending downwardly from a lower end of the container 1 to the refrigerant heater 4 and an outlet pipe 6 extending from the refrigerant heater 4 to the gas-liquid separating chamber 2 of the container 1, thus constituting a heating circuit. The opening of the outlet pipe 6 is positioned in an upper portion of the gas-liquid separating chamber 2.
The container 1 is also fluid-connected with a radiator 14 having a fan 15 via a gas feeding pipe 16 extending upwardly from an upper portion of the container 1, a liquid-return pipe 18, a second check valve 17, a liquid-receiving container 7 disposed above the container 1, and a liquid-dropping pipe 10 having a first check valve 11, thus constituting a heat release circuit.
A horn-shaped pipe 13A formed on the lower end of an equalizing pipe 13 has an opening within the container 1 and is disposed above the upper end of the outlet pipe 6. An upper end of the equalizing pipe 13 is communicated with the inlet of an electromagnetic valve 12. The outlet of the electromagnetic valve 12 is communicated with an upper portion of the liquid-receiving container 7. The upper portion of the liquid-receiving container 7 has a liquid-receiving chamber 8 defined therein and incorporating a porous sheet 9, while the lower portion thereof is formed into, or otherwise integrated with, the refrigerant-dropping pipe 10 accommodating the first check valve 11. The lower end of the dropping pipe 10 is communicated with the gas-liquid separating chamber 2 in the container 1. The equalizing pipe 13, the electromagnetic valve 12, and the dropping pipe 10 constitute a liquid refrigerant-dropping circuit.
The timing at which the electromagnetic valve 12 is opened or closed is controlled by a control section 22 based on an output signal from a burner combustion controller 20 for the burner 19 and that from a temperature detector 21 mounted on the outlet pipe 6.
In this construction, the liquid refrigerant 3 heated by the burner 19 flows into the container 1 in a mixed state of gas and liquid via the outlet pipe 6 and is then separated into gas refrigerant and liquid refrigerant within the container 1. The liquid refrigerant is stored in the container 1 and is then circulated to the refrigerant heater 4 via the inlet pipe 5. The gas refrigerant which has flowed into the gas-liquid separating chamber 2 from the refrigerant heater 4 is fed to the radiator 14 via the gas feeding pipe 16 and is cooled by the fan 15.
The gas refrigerant so cooled during its passage through the radiator 14 is condensed and subcooled by the radiator 14. When the electromagnetic valve 12 is closed at this time, the liquid-receiving chamber 8 is closed because the first check valve 11 is normally biased upwardly by a spring 11A. Thus, the refrigerant flow in the heat release circuit is cut off temporarily with the closure of the electromagnetic valve 12.
However, when the pressure of the subcooled liquid refrigerant attains a value slightly higher than that in the liquid-receiving chamber 8, the subcooled liquid refrigerant enters the liquid-receiving chamber 8 through the liquid-return pipe 18 and the second check valve 17. The liquid refrigerant which has entered the liquid-receiving chamber 8 is diffused by the porous plate 9, thus condensing the gas refrigerant in the liquid-receiving chamber 8. Consequently, the pressure in the liquid-receiving chamber 8 drops rapidly.
For example, assuming that saturated gas of 60.degree. C. is present in the liquid-receiving chamber 8 and that liquid refrigerant (the degree of subcooling: 30.degree. C.) in the radiator 14 flows into the liquid-receiving chamber 8 from the radiator 14, the pressure in the liquid-receiving chamber 8 drops by 5 to 6 kg/cm.sup.2 G from a saturation pressure of 24kg/cm.sup.2 G (HCFC 22) of 60.degree. C.
As a result, the liquid refrigerant in the radiator 14 is sucked and fed into the liquid-receiving chamber 8 having a reduced pressure, thus filling the liquid-receiving chamber 8. When the electromagnetic valve 12 is subsequently opened upon the passage of a predetermined time, the gas-liquid refrigerant jetted from the outlet pipe 6 is introduced into the liquid-receiving chamber 8. Due to the gravitational effect of the refrigerant and the dynamic pressure component generated by the gas flow of the gas-liquid refrigerant from the outlet pipe 6, the liquid refrigerant in the liquid-receiving chamber 8 flows into the container 1 via the first check valve 11 then opened against the urging force of the spring 11A. At this time, the second check valve 17 is in a closed state because the pressure in the liquid-receiving chamber 8 is high.
When the electromagnetic valve 12 is closed a predetermined time after the opening thereof, the pressure in the liquid-receiving chamber 8 drops. As a result, the first check valve 11 is closed by the urging force of the spring 11A and the subcooled liquid refrigerant in the radiator 14 is then introduced into the liquid-receiving chamber 8 to fill up the liquid-receiving chamber 8 with the liquid refrigerant. The electromagnetic valve 12 is opened when a predetermined time has elapsed.
The foregoing cycle of operation is repeated. That is, the heating circuit including the refrigerant heater 4 transfers heat by a natural circulation mode, whereas the heat release circuit including the radiator 14 transfers heat by an intermittent mode.
In the above construction, the amount G (kg/h) of refrigerant circulated is expressed as follows: EQU G=(V.times..gamma..times.3600)/(T.times.1000) (1)
where V is the volume (cc) of the liquid-receiving chamber; .gamma. is the density (g/cc) of the liquid refrigerant in the liquid-receiving chamber; and T is the cycle (open time+closed time) (sec) of opening and closure of the electromagnetic valve.
The amount Q (kcal/h) of heat transfer is expressed as follows: EQU Q=.DELTA.i.times.G (2)
where .DELTA.i (kcal/kg) is the difference between the enthalpy of refrigerant at the inlet of the radiator 14 and that of refrigerant at the outlet thereof.
The cycle T is found as follows from equations (1) and (2) above: EQU T=(.DELTA.i.times.V.times..gamma..times.3600)/(Q.times.1000)(3)
From the above, the cycle T is proportional to .DELTA.i and inversely proportional to the combustion amount of the burner 19, namely, the amount Q of heat transfer. This indicates that it is necessary to adjust the amount G of refrigerant circulation according to the amount of combustion so that the cycle T may become short when the amount of combustion is large, and the cycle T may become long when the amount of combustion is small. Due to the characteristic of the refrigerant, .DELTA.i becomes small when the pressure in the radiator 14 is high, whereas .DELTA.i becomes large when the pressure in the radiator 14 is low. Therefore, it is also necessary to adjust the amount G of refrigerant circulation in accordance with the pressure in the radiator 14 as well, so that the cycle T may become short when the pressure in the radiator 14 is high, and the cycle T may become long when the pressure in the radiator 14 is low.
To this end, based on an output signal from the controller 20 for controlling the amount of combustion and that from the temperature detector 21 mounted on the outlet pipe 6 through which the gas-liquid refrigerant having a correlation between the pressure and temperature thereof flows, the timing at which the electromagnetic valve 12 is opened or closed is controlled by the control section 22.
The conventional heat transfer apparatus having the above construction has, however, the following problems in heat transfer performance:
(1) As described above, the conventional heat transfer apparatus is such that the refrigerant in a mixed state of gas and liquid jetted from the outlet pipe 6 is introduced into the liquid-receiving chamber 8, with the electromagnetic valve 12 opened, and the liquid refrigerant stored in the liquid-receiving chamber 8 is dropped into the container 1 by the dynamic pressure component generated by the gas-liquid refrigerant jetted from the outlet pipe 6 in addition to the gravitational effect of the liquid refrigerant.
However, when the liquid refrigerant is dropped into the container 1, the refrigerant containing a liquid component is introduced into the liquid-receiving chamber 8 via the equalizing pipe 13. Thus, when the electromagnetic valve 12 is subsequently closed and when the first check valve 11 is closed by the spring 11A, the liquid refrigerant remains in the liquid-receiving chamber 8, thus reducing the effective volume of the liquid-receiving chamber 8 and the amount of refrigerant to be fed from the radiator 14 to the liquid-receiving chamber 8.
(2) When the subcooled liquid refrigerant flows into the radiator 14 from the liquid-receiving chamber 8 and if warm liquid refrigerant remains in the liquid-receiving chamber 8, the cooling capability of the subcooled liquid refrigerant is used to condense the gas refrigerant in the liquid-receiving chamber 8 to thereby reduce the pressure inside the liquid-receiving chamber 8, and is also used to lower the temperature of the liquid refrigerant which has remained therein. Therefore, the pressure in the liquid-receiving chamber 8 cannot be reduced greatly and, hence, it takes a long time to suck the liquid refrigerant into the liquid-receiving chamber 8 from the radiator 14.
Further, because opposite ends of the refrigerant-dropping pipe 10 are soldered or welded to the liquid-receiving chamber 8 and to the container 1, it is necessary to lengthen the refrigerant-dropping pipe 10 to prevent a thermal deformation of the first check valve 11 during soldering or welding. Because of this, the resistance to the flow of the liquid refrigerant is high and, hence, it takes a long time to drop the liquid refrigerant from the liquid-receiving chamber 8 to the container 1.
For these reasons, the conventional heat transfer apparatus is incapable of transferring a large quantity of heat.
(3) It is to be noted that the heat release performance can be maximized and the required amount of circulation of the refrigerant can be minimized if only the gas refrigerant from the gas-liquid separating chamber 2 is introduced into the radiator 14 to accomplish a heat exchange of latent heat.
In the conventional heat transfer apparatus, however, the gas-liquid refrigerant jetted from the outlet pipe 6 of the refrigerant heater 4 is directed upwardly and subsequently downwardly in synchronization with the opening and subsequent closure of the electromagnetic valve 12. As a result, droplets scatter in the gas-liquid separating chamber 2, thus forming a turbulent flow. The droplets eventually enter the gas feeding pipe 16 and circulate through the heat release circuit. This reduces the heat exchange efficiency and increases the amount of refrigerant contained in the entire apparatus. Further, it is necessary to circulate refrigerant that does not contribute to heat exchange of latent heat to be performed by the radiator 14.
Furthermore, the liquid refrigerant-dropping circuit is positioned above the container 1, and opposite ends of the refrigerant-dropping pipe 10 are joined to the liquid-receiving chamber 8 and to the container 1. Thus, it is necessary to provide the long refrigerant-dropping pipe 10 to prevent heat generated during joining from deforming the first check valve 11, resulting in an increase in height from the bottom of the container 1 to the top of the electromagnetic valve 12.
Accordingly, the conventional heat transfer apparatus cannot be made compact, requires a considerable number of parts, and has many portions to be joined. Thus, the cost of manufacturing the apparatus is high.